This invention relates generally to controlling power to the subsystems of a construction machine and particularly to distributing available power to the machine subsystems by using a power management controller responding to predetermined priorities and operational requirements. In the example given, the invention relates to the implement and drive train subsystems of a construction machine.
In operating construction machinery the available power, typically provided by an internal combustion engine, is mainly consumed by three major systems; namely, a power steering system, an implement control system and a power train system for propulsion. For safety reasons, it is typical for the steering system to be given first priority to available power. The remaining power is available for consumption by the implement operating system and the power train system.
In operating a wheel loader to load rock in a raised hopper of a rock crusher, the wheel loader scoops up a bucket load of raw material and travels toward the hopper with the bucket relatively low in interest of visibility and machine stability. Although some rock crusher hoppers are located on level ground, it is common practice to build a loading ramp to the hopper, the length and grade of which varies from site to site. As the loader approaches the hopper, the operator raises the bucket in anticipation of dumping the load when the hopper is reached. Thus the implement operating system and the power train system are simultaneously consuming power.
In prior power management systems the implement operating system is given priority to the available power for the power train system; however, the available power for the power train may be so limited as to produce excessively slow travel speed when raising the bucket and traveling up a relatively steep loading ramp. Excessively slow speed reduces operating efficiency of the wheel loader. Control systems heretofore provided for construction machinery have not allocated power to implement and power train systems to ensure their simultaneous operation in an acceptable manner.
In U.S. Pat. No. 5,525,043 issued Jun. 11, 1996 to Michael S. Lukich for a Hydraulic Power Control System, a method and apparatus are described for controlling a hydraulic control system in a hydraulic excavator to limit engine lug. The displacement of a hydraulic pump driven by the engine is reduced in response to the engine load increasing above a predefined level to prevent the engine from stalling. This method and control apparatus would not provide satisfactory minimum/maximum allocation of power to implement and drive train systems such as used in wheel loaders.
U.S. Pat. No. 6,047,545 issued Apr. 11, 2000 to Horst Deininger for Hydrostatic Drive System discloses a lift truck power system in which a hydraulic steering system is given first priority, a hydraulic work system is given second priority and a hydrostatic drive system is given third priority. This and other priority systems employed in wheel loaders give rise to the problem of excessively slow travel speed when traveling with a load of rock up a loading ramp to a rock crusher hopper and simultaneously raising the bucket in anticipation of dumping the raw material in the hopper.
U.S. Pat. No. 5,295,353 issued Mar. 22, 1994 to M. Ikari for a Controlling Arrangement for Travelling Work Vehicle illustrates and describes a wheel loader having a torque converter and two fixed capacity hydraulic pumps supplying pressure fluid to the valves controlling boom lift and bucket tile actuators. One of the two hydraulic pumps is unloaded when the accelerator pedal is at full throttle and the engine speed is under a predetermined speed. Although this control system provides a change in allocation of power when the engine does not increase speeds in response to a requested speed increase, the control does not provide for adjustment of the power allocations to the implement and power train subsystems based on the operator""s desired commands.
The present invention is directed to overcoming one or more of the problems as set forth above.
In one aspect of the present invention, the available power, after satisfying vehicle steering requirements, is allocated to an implement subsystem and power train system.
The allocation of power to the implement subsystem and the power train subsystem is controlled by a power management system which is programmed to allocate a quantity of available power to the implement subsystem, such quantity falling between predetermined maximum and minimum percentages of the available power depending on the difference between desired travel speed and actual travel speed.
The maximum and minimum percentages of the available power allocated to the implement subsystem may be adjusted to provide efficient machine performance for particular machine work assignments. Adjustable set points are preferably provided to establish the minimum difference between the desired and the actual travel speed at which the maximum percent of available power is allocated to the implement subsystem and to establish the maximum difference in the desired and the actual travel speed at which the minimum percent of available power is allocated to the implement subsystem. An on-board compute is programmed to provide a smooth change in power allocation to the implement subsystem as changes occur in the difference between requested travel speed and actual travel speed.